Injection device with dose interruption fail safe

ABSTRACT

A dose setting mechanism is provided that includes a dose knob, a dose selector, a radial projecting rib and a snap element. The radial projecting rib is positioned circumferentially on an inside surface of the dose selector. The snap element includes a protrusion. The protruding rib has a reduced section that allows the protruding rib to move axially relative to the protrusion to initiate dose delivery.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 16/037,829, filed Jul. 17, 2018, the content of which is herebyincorporated by reference.

BACKGROUND Technical Field

The present disclosure relates to an injection device and particularlyto the dose setting mechanism of the injection device, where a user canselect one or more predetermined fix dose settings as a direct result ofthe design and manufacture of a single component of the dose settingmechanism. Changing the design of this single component of the dosesetting mechanism allows for the efficient manufacture of injectiondevices that can be custom made for a specific dosing regimen and/orused in dose-ranging evaluations.

Background Information

There are a number of medicament delivery devices on the market that arecapable of automatically, semi-automatically or manually deliveringdoses of medicament. Of the known type of delivery devices the“pen-type” injector is gaining in popularity and is available in bothreusable and disposable designs. Such devices are constructed with dosesetting mechanism that include a variety of inter-acting components forobtaining desired functions, such as setting a dose and then deliveringthe set dose. In most cases, these medicament delivery devices have onlyone or two single fixed dose setting or variable dose setting where eachpossible set dose must be a multiple of the lowest possible set dose. Inother words, these existing variable dose injection devices do not allowa dose to be set that is a fraction of the lowest possible dose.

The types of pen-type injector designs have a dose setting mechanismlocated at the distal end of the device and a medicament container, suchas, a cartridge, located in the proximal end. The known injector designstypically are multiple (variable) dose devices, meaning that the usercan select (dial) a dose between O and a maximum allowable settabledose. A dose dial sleeve is printed with a range of possible dosesettings that typically correspond to each possible incremental dosesetting. For example, if the injector is designed and manufactured witha maximum dose setting of 80 international units (IU), then eachincremental settable dose differs by one IU. Stated differently, to seta dose of 60 IU, the user would rotate a dose setting knob through 60possible dose settings while viewing the dose dial sleeve markingindicating each incremental dose until it showed 60 IU. Of course, therewould be nothing to prevent a user from accidentally setting an underdose of 59 IU or an over dose of 61 IU, especially if the user isphysical impaired, for example reduced eyesight or severe arthritis.

As stated, some injection devices are manufactured and designed asso-called fixed dose designs where the dose dial sleeve containsprinting signifying only one or two doses. The design idea behind thesedevices is for the user is to rotate the dose setting knob until one ofthe fixed dose setting is observed, typically in a window of theinjector housing. However, in such injector designs the user is stillrequired to step through individual equal incremental dose settingsuntil the indicia of the fixed dose setting is observed in the window.Because the dose setting mechanism requires the user to physically stepthrough each incremental dose setting there is nothing to prevent theuser from stopping at dose less than or greater than the fixed dosesetting. In addition, the user will experience a haptic or audiblenotification as the dose setting mechanism is dialed through eachincremental dose to arrive at the final dose setting.

Another drawback of the existing injector designs is the inability tohave fixed doses that are not multiples of a single incremental value.In other words, if an injector is designed with a maximum settable doseof 80 IU, then typically each incremental dose would be I IU. As such,it would not be possible to set a dose of 2.3 IU. The use could only seta dose of 2 or 3 IU. Stated another way, fractional doses could not beset with such a dose setting mechanism. The ability to set fractionaldoses is important, especially during studies trying to determineoptimum dose amounts for newly developed medicaments and/or for newpatients using existing medicaments for the first time.

Although there exist many drug delivery devices available for patientuse, there is clearly a need to have an injector available that candeliver one or more predetermined fixed doses where at least one of thepredetermined fixed doses is a fractional amount of a secondpredetermined fixed dose. The availability of a pen-type injector wherethe user cannot set and/or deliver a dose that is not one of a number ofpredetermined fixed doses is also an important goal. And, it is highlydesirable to have an injector design where only a single mechanicalcomponent of the dose setting mechanism needs to be redesigned andmanufactured in order to change or vary the predetermined fix doses.This would allow cost effective manufacturing of injection devices thatcould be easily customized for patients to allow the injection of one ormore effective doses of medicament specifically tailored to theparticular user.

The disclosure presented below solves the above-mentioned problems withexisting medicament delivery devices and provides an injector designthat fulfills the needs and requirements mentioned above.

SUMMARY

This disclosure presents a number of dose setting mechanism designs thatallow an injection device to be set with one or more fractionalpredetermined fixed dose settings. The designs can also prevent thesetting of an unintended dose, i.e., a dose other than one of thepredetermined fixed dose settings. The dose setting designs provide acost effective way of manufacturing an injection device because only asingle component needs to be redesigned and manufactured in order toprovide a complete injection device having one or more differentpredetermined fix doses.

In one embodiment the dose setting mechanism includes a floating spline,a dose knob, a dose selector, and a snap element. The floating spline isrotationally engaged with the snap element, which has a fixed set ofsplines. The floating spline is engaged with a corresponding set ofsplines on the dose selector during dose setting and dose delivery. Thefloating spline comprises a plurality of longitudinally extendingsplines that are engaged with splines on the dose knob during dosedelivery, but not so engaged during dose setting. The floating splinecan also be axially fixed relative to the snap element.

The snap element rotates relative to the floating spline and the doseselector during both dose setting and dose delivery. This is due to thefloating spline being rotationally fixed to the dose selector throughcorresponding splines on an inner surface of the dose selector. Sincethe dose selector is rotationally fixed to the housing through a splinedconnection, the engagement and meshing of the floating spline with thesplines on the inner surface of the dose selector prevents rotation ofthe floating spine relative to the body during dose setting and dosedelivery. The snap element is also configured with a flexible arm thathas a radial extending protrusion that preferably projects outwardly into engage a plurality of dose stops that are located on an inner surfaceof the dose selector. These dose stops are designed and manufactured,preferably through a molding process, to be spaced radially apart fromeach other such that they define a set of finite predetermined fixeddoses. During the setting of one of the predetermined doses, the snapelement is rotated relative to the dose selector to cause the protrusionon the snap element to engage with and travel over one of the dosestops. Once the protrusion travels over the dose stop and rotation isstopped this position of the snap element defines a single fixed dose ofmedicament for delivery. The set of finite predetermined fixed dosesincludes a lowest fixed dose and one or more higher fixed doses.

The distance between the dose stops on the inner surface of the doseselector can be designed and manufactured such that the one or morehigher fixed doses is not equal to an even multiple of the lowest fixeddose. This results in a fixed dose setting that includes a fractionalamount of the lowest fixed dose. Stated differently, the distancebetween the dose stops can be manufactured, i.e., predetermined, suchthat at least one of the one or more higher fixed doses is equal to thelowest fixed dose plus a fractional amount of the lowest fixed dose.This is not possible with dose setting mechanisms currently known.

Because the finite predetermined fixed doses are defined only by thenumber of and relative spacing between dose stops, and those dose stopsare uniquely located on a single component of the dose settingmechanism, i.e., the dose selector, this presents an efficient and costeffective method to change the set of finite predetermined fixed doseswithout manufacturing any other components of the dose settingmechanism. In other words, only the design of dose selector needs to bechanged to result in the manufacture of a second dose selector, whichcan then replace the original dose selector during assembly of theinjection device. No other components of the dose setting mechanism needreplacement. In some cases, the printing that appears on a dose sleevemay be changed, but the design and manufacture of the dose sleeveremains the same. Replacement of the original dose selector with asecond dose selector having a different arrangement of dose stopsresults in the dose setting mechanism having a different set of finitepredetermined fixed doses.

The spatial relationship between the dose selector and the snap elementchanges between dose setting and dose delivery. There is a first fixedrelative axial position between the snap element and the dose selector,which occurs during dose setting and there is a second fixed axialrelative position that occurs during dose delivery. In the first fixedposition, the protrusion can engage a dose stop. However, in the secondfixed position the protrusion cannot engage a dose stop, wherein thefirst fixed relative position is achieved during dose setting and thesecond fixed relative position is achieved during dose delivery. At thecompletion of the dose delivery, the protrusion may engage with andtravel over an end of injection bump to provide the user with a tactileand/or audible notification that the delivery is complete.

As mentioned, the dose setting mechanism of this disclosure can includea functional and structural feature that prevents a user from setting adose other than one of the predetermined fixed doses, i.e., a so-calledunintended dose. This fail-safe feature of the present disclosureprevents the setting of a dose other than one of the finite set ofpredetermined fixed doses by using a biasing member that exerts acounter rotation force on the snap element during the dose settingprocedure. The biasing member can be a torsion spring operativelyconnected to the snap element through a connection with a dose sleeve.When a torsion spring is incorporated in the dose setting mechanism itis biased to a predetermined torque during assembly. The torque exerts aforce on the snap element such that during dose setting by a userdialing or rotating the dose knob, the snap element is urged to resistthe rotational force applied by the user. Although this counterrotational torque is easily overcome by the user during the rotation ofthe dose knob, if the user were to release the dose knob for some reasonthe torque would cause the knob and the snap element to rotate in theopposite direction. In such an event, the torque is preferablysufficient to counter-rotate the snap element such that the protrusionwill return to and engage with a previous dose stop. In some instances,it may be desirable to use a biasing member that will counter rotate thesnap element such that the protrusion will travel back to the zero dosehard stop. The fail-safe feature would only come into play if a user didnot rotate the dose knob and snap element far enough so that theprotrusion engages and travels over a next dose stop that corresponds toa higher fixed dose than the previous dose stop. As the dose knob isrotated during dose setting and the snap element engages successive dosestops, the torque exerted by the torsion spring increases.

In some instances, it may be desirable to select a biasing member thatexerts only enough torque to counter-rotate the snap element to the nextlowest dose stop. In such cases, the biasing member will not add anymechanical assistance to the user during the dose delivery procedure.There may also be situations where it is desirable to select and use abiasing member that develops enough torque during dose setting thatduring dose delivery a mechanical assistance through a counterrotational force is achieved such that a user needs to apply less axialforce than would be needed using a biasing member with inherently lesstorque.

The dose knob is operatively connected to the snap element through a setof splines located on an inner surface of the dose knob. These splinesengage and mesh with the fixed set of splines on an outer surface of thesnap element during dose setting. The rotation of the dose knob duringdose setting causes rotation and axial movement of the snap element andonly axial distal movement of the dose selector. The snap elementtranslates axially relative to the housing in the distal directionbecause the snap element is rotationally fixed to the dose sleeve, whichin turn is threadedly connected to an inner surface of the housing. Thedose selector does not rotate relative to the housing because it issplined to housing such that it can only move axially relative to thehousing. The dose knob is axially fixed to the dose selector, but canrotate relative to the dose selector so that the dose knob, doseselector, dose sleeve and the snap element all move axially relative tothe housing during both dose setting and dose delivery.

The snap element has a second set of splines attached to the outersurface of the snap element. This second set of splines or floatingspline are a separate component of the dose setting mechanism and arenot an integral part of the snap element, i.e., they are notrotationally fixed to the snap element. The floating spline ispreferably circumferentially located around an outer surface of the snapelement in a free-wheeling fashion such that when the floating spline isrotationally fixed relative to the housing, the snap element will rotatewithin or relative to the floating spline. The floating spline isconfigured with a plurality of radial projecting longitudinal splinesequally spaced apart from one another. This in contrast to the dosestops on the inner surface of the dose selector, where the spacesbetween the dose stops do not have to be equal. However, the spacebetween each of the dose stops is a multiple of the space between eachof the radially projecting longitudinal splines of the floating splinecomponent.

To deliver a set dose the user will exert an axial force in a proximaldirection relative to the housing on the dose knob. If this axial forceis stopped, a halted dose delivery situation can arise. The dose settingmechanism of the present disclosure contains a second fail-safe featureto prevent possible problems associated with a halted dose deliverysituation. As will be explained in more detail below, the initiation ofthe dose delivery procedure first involves an axial movement of the doseknob and the dose selector, which is axially fixed to the dose knob.This axial movement of the dose knob also causes disengagement of thesplines on the dose knob from the fixed splines on the snap element.This disengagement removes the rotationally fixed relationship betweenthe dose knob and the snap element that exists during the dose settingprocedure. The proximal axial movement of dose knob and dose selectorthat occurs during the initiation of the during dose delivery procedureis relative to the housing and, at least initially, relative to the snapelement. The axial proximal movement of the dose selector causes thedose stops to move out of radial alignment with the protrusion on thesnap element. The dose knob and dose selector are biased in a distaldirection relative to the snap element by a second biasing member, whichpreferably is a compression spring. During dose setting this secondbasing member ensures that splines on the dose knob are engaged with thefixed splines on the snap element. However, during dose delivery thedistally directed biasing force exerted by the second biasing member isovercome by the user's proximally directed axial force on the dose knob,thus allowing disengagement of the splines.

As stated, during dose delivery, the user exerts a counter axial forcein the proximal direction to move the dose knob and dose selectoraxially relative to the snap element. If the injection is halted and theaxial force in the proximal direction is removed or sufficientlydecreased, the second biasing member will urge the dose selector back inthe distal direction causing the protrusion and the dose stops to comeback into alignment and causing the splines on the dose knob to reengagethe fixed splines on the snap element. Because the snap element issubject to a counter rotation force from the first biasing member, thiswill tend to cause both the snap element and the dose knob to rotate ina direction that will reduce the set dose to an unintended, and likelyunknown, lower amount. Stated differently, the counter rotation of thesnap element will cause the protrusion to rotate to engage the nextlower predetermined dose stop. As will be explained in more detailbelow, the rotation of the snap element also causes rotation of a nutengaged with a piston rod where the position of the nut relative to thepiston rod is directly proportional to an amount of medicament to bedelivered. Allowing the counter rotation of the snap element in a haltedinjection situation act to reduce the intended previously set dose by anamount that may not be determined by the user, thus resulting in apotential dangerous under dosing situation.

The second fail-safe feature of the dose setting mechanism of thisdisclosure can be achieved in a variety of designs, preferably involvingthe use of a radially projecting circumferential rib that engages eitherthe first protrusion or a second protrusion on the snap element suchthat the dose selector can only be pressed and moved in a proximaldirection to start a dose delivery when the second protrusion is alignedwith a cut-out in the radially projecting rib. This axial proximalmovement of the dose selector at the start of the dose delivery movesthe radially projecting rib from a first position where the secondprotrusion is located on the proximal facing side of the rib to a secondposition. In moving to the second position the rib moves relative to thesecond protrusion such that the cut-out moves past the second protrusionso that it is then positioned on the distal facing side of the rib.Preferably, the radially projecting rib has a plurality of cut-outs thatcorrespond to each of the dose stops. Once in the second position therib now can block distal axial movement of dose selector as the snapelement begins to counter rotate as dose delivery proceeds if the userreleases the proximal directed force on the dose knob. The axialblocking feature occurs because the second biasing member urges the doseselector in the distal direction thus causing an abutment of the secondprotrusion with the distal facing surface of the rib. This abutmentprevents further movement of the dose selector and thus re-engagement ofthe fixed splines with the splines on the inside of the dose knob.

The second fail-safe feature therefore allows the dose selector to onlymove in a distal direction during dose delivery when the secondprotrusion is aligned with a cut-out in the radially projecting rib. Ifa halted injection occurs when a cut-out in the rib corresponds oraligns with the position of a dose stop, a distal axial movement of thedose selector will occur, but such movement will realign the firstprotrusion with the corresponding dose stop and will reengage the fixedsplines with the dose knob. Since the first protrusion is now re-engagedwith a dose stop there can be no counter rotation of the snap elementand dose knob relative to housing, and thus no rotation of the nutrelative to the piston. The result being there is no reduction in theset dose. Another benefit of this second fail-safe feature is that thedose knob can only move axially relative to the snap element when theprotrusion on the snap element is engaged with one of the dose stops ofthe dose selector. This would prevent an unintended dose delivery if theuser were to rotate the dose knob while simultaneously exerting an axialdriving force in the proximal direction.

The snap element can also include a clicker arm that engages the radialprojecting longitudinal splines on the inner surface of the doseselector during dose delivery such that the rotation of the snap elementproduces an audible feedback as the clicker arm travels over the radialprojecting longitudinal splines. During dose setting, the engagement ofthe first protrusion on the flexible arm of the snap element with thedose stops generates a first number of tactile and/or audiblenotifications. During dose delivery, a second number of tactile and/oraudible notifications is generated, where the second number ofnotifications is greater than the first number. In some instances, thesecond number of notifications is equal to the total number of thesplines that correspond to the set predetermined fixed dose. The degreeof tactile notification and/or the level of audible notification can bechanged by changing the shape and/or the type component materials thatare used to fabricate the splines or the clicker arm. Similarly, thedose stops and the first protrusion on the flexible arm can beconfigured with various shapes or materials of construction to generatedistinct tactile and/or audible notifications so that a user willreadily discern the difference between dose setting/dose cancelling anddose delivery.

The dose setting mechanism of this disclosure also can contain a clutchthat is operatively connected to the dose knob at a distal end of theclutch. In one embodiment, the proximal end of the clutch isrotationally fixed to a nut and is axially slidable relative to the nut.The nut can be threadedly engaged with a piston rod that is configuredto move only axially in the proximal direction such that during dosedelivery the piston rod exerts an axial force causing a plunger withinthe container of medicament to move proximally pressurizing themedicament so that it is discharged through a proximal opening in themedicament container. A preferred shape of the piston rod includes onehaving a non-circular cross-section and having threads on the outsidesurface. The pitch of these threads is directly proportional to eachpredetermined fixed dose of medicament. A piston guide having anon-circular center opening can be included in the dose settingmechanism, where the piston guide accepts the non-circular cross-sectionof the piston rod such that the piston guide prevents the piston rodfrom rotating during both dose setting and dose delivery.

The dose setting knob and clutch are operatively connected such thatthey are rotationally fixed to each other so that during dose settingrotation of the dose knob rotates the clutch, which in turn rotates thenut. Rotation of the nut causes the nut to translate axially in a distaldirection along threads located on the outer surface of the piston rodduring dose setting and to translate in the proximal direction duringdose cancellation. During dose delivery, the dose knob is prevented fromrotating due to the engagement with the floating spline that isrotationally fixed to the housing. As the clutch is rotationally andaxially fixed to the dose knob, the clutch likewise does not rotate andcan only move axially in the proximal direction during dose delivery. Assuch, the nut also does not rotate during dose delivery, moving onlyaxially with the piston rod a distance in a proximal direction. Thisdistance is directly proportional to the set dose. This axial onlymovement of the nut necessarily causes axial movement of the piston rodbecause of the threaded engagement with the nut. As mentioned, duringdose setting the axial translational movement of the nut in the distaldirection is directly proportional to an amount of the medicament thatwould be delivered if the piston rod was then moved proximally withoutrotation of the nut relative to the piston rod.

The dose setting knob can also include an anti-rolling feature thatprevents the injection device from rolling when a user places the deviceunattended on a flat surface, such as a table top. To prevent the devicefrom rolling and falling off a surface where the device could bedamaged, the dose knob can include a radially projecting rib. This ribprevents the injection device from rolling greater than 180 degrees whenthe device is placed on a flat surface. The radially projecting rib doesnot point to, or aligned with, a corresponding designation on the bodyof the device. In other words, the relative circumferential position ofthe rib as the dose knob is turned to set a dose does not correlate withany of the finite set of predetermined fixed doses. To set a dose, theknob is always turned in one direction, for example: clockwise. The knobdoes not turn during injection. So, with each injection the knob and, assuch, the radially projecting rib turns further clockwise. As such, theradial position of the rib cannot correlate with any part of the penbody, in particular not with the predetermined doses.

This disclosure is also directed to complete injection devices. Onepossible embodiment of such an injection device includes a body with anattachment mechanism at a proximal end configured to connect with aholder for a container, preferably a cartridge, containing a medicamentto be delivered to a patient in a series of set doses. A dose settingmechanism as described above can be used in this injection device wherethe dose selector is configured to allow only a set of finitepredetermined fixed doses to be set by a user of the device, where theset of finite predetermined fixed doses includes a lowest fixed dose andone or more higher fixed doses, and wherein at least one of the one ormore higher fixed doses is equal to the lowest fixed dose plus afractional amount of the lowest fixed dose. The dose stops arecircumferentially positioned on an inner surface of the dose selectorand the circumferential distance between each dose stop and a zero dosehard stop is directly proportional to each fixed dose.

In another embodiment of the injection device of this disclosure thedevice has a body with an attachment mechanism at a proximal endconfigured to connect to a cartridge holder that is designed to hold acartridge containing a quantity of medicament, where the quantity ofmedicament is measured in doses. The device further includes a dosesetting mechanism having a dose selector rotatably fixed to the body,where the dose selector contains dose stops configured to allow only afinite set of predetermined fixed doses that can be set using the dosesetting mechanism. There is also a snap element that is rotatablerelative to the dose selector. The snap element has a fixed set ofsplines integral to an outer surface and arranged circumferentiallyaround the outer surface. The dose setting mechanism further contains afail-safe component configured to prevent a user of the injection devicefrom setting a dose other than one of the finite set of predeterminedfixed unit doses. A floating spline that is axially fixed to the snapelement allows the snap element to rotate relative to the floatingspline during both dose setting and dose delivery. A dose knob having afirst position during dose setting and a second position during dosedelivery allows a user to select one of the predetermined fixed doses,where in the first position the dose knob is splined to the fixed set ofsplines but not splined to the floating spline and when in the secondposition the dose knob is splined to the floating spline but not thefixed set of splines.

The present disclosure also is directed at methods of designing andmanufacturing an injection device based on performing a dose-rangingevaluation. This is possible because of the unique design of the dosesetting mechanism where only a single component, namely the doseselector, needs to be replaced with a different dose selector in orderthat the injection device has a new finite set of predetermined fixeddoses or just a single predetermined effective fixed dose. One suchmethod includes providing a first injection device having a first dosesetting mechanism that includes a floating spline, a dose knob, a doseselector, and a snap element as described above. The floating spline isengaged with a fixed set of splines on the dose selector during dosesetting and dose delivery. Additionally, the floating spline is engagedwith splines on the dose knob during dose delivery, but not during dosesetting. This first injection device is then used in a dose-rangingevaluation trial where a plurality of the first injection devicecontaining a medicament are distributed to a plurality of trialpatients.

The trial patients are instructed to use the first injection devices toperform injections of predetermined doses of the medicament.Physiological data may be collected from the trial patients after theinjections are performed in order to analyze the collected physiologicaldata to determine an effective single dose of the medicament.Alternatively, the trial patients may simply report the effects of theinjections of the predetermined doses. Based on the analyzed or reportedresults, a second injection device can be provided that has beenmanufactured with a second dose setting mechanism where themanufacturing process involves redesigning the dose selector such thatthe second injection device can be set to a new finite set ofpredetermined doses or to a single effective fixed dose. The floatingspline, the dose knob, and the snap element in the second dose settingmechanism are unchanged in design from that used in the first dosesetting mechanism. In other words, only the dose selector must beredesigned and newly manufactured. All other components used to assemblethe second dose setting mechanism remain identical to those use in thefirst dose setting mechanism. In some cases, indicia printing on theoutside surface of the dose sleeve may be changed to reflect newpredetermined dose setting(s) of the redesigned and newly manufactureddose selector. However, the design, manufacture, and functionality ofthe dose sleeve remains unchanged.

Another advantage of the dose setting mechanism of the presentdisclosure that is related to the fact that only a single componentneeds to be changed to affect a new set of finite predetermined dosesettings is that the equipment used for assembly of the completeinjection device and the methodology for assembly remains the same.Keeping the same assembly equipment and methodology is directly relatedto the fact that only the number and location of the dose stops insidethe dose selector needs to be changed to arrive at a new injectiondevice.

The above described advantage is directly related to the inherentflexibility of the design of the dose selector to achieve any possiblenumber of predetermined fixed dose settings between a zero dose and amaximum dose, including fractional doses of the lowest set dose. Thisbecomes important for a pharmaceutical company that wants to evaluate anew medicament or to evaluate how an existing medicament will impact adifferent disease state. Especially beneficial is the ability to easilyand efficiently design different dose selectors each having a differentfinite set of predetermined doses, including having fractional fixedpredetermined doses instead of having each fixed dose being a multipleof a lowest fixed dose.

In injection devices of the type disclosed in this disclosure themanufacture of those devices may bring unavoidable tolerances andfunctional clearances between the single components of the drug deliverydevice, in particular the components of the dose setting mechanism. As aconsequence, clearances such as a gap between those components, such asbetween the piston rod foot and the sliding piston may occur even afterthe drug delivery device has been assembled so that the piston may notbe in contact with the distal end of the foot. It is, therefore,important to eliminate any such gaps or manufacturing toleranceanomalies so that the dose setting mechanism is in a pre-stressed stateprior to the first setting of one of the finite predetermined set doses.If this is not achieved, then it would be possible that the dialedpredetermined set dose may not be accurately dispensed from the devicecorrectly. Initial manufacturing clearances may already falsify thesetting of the dose. To adjust the drug delivery device for use, primingactions are conducted to ensure that the drive mechanism is correctlyadjusted, e.g. that the piston rod and the attached foot is in contactwith the sliding piston so that the correct amount of the medicament canexpelled from the device. These adjustment actions can be achieved ineither the manufacturing/assembly procedure of the device or by the userof the assembled device immediately prior to the first use of thedevice. In the latter scenario the user will need to dispense a smallamount of medicament, which gives a visual indication that the drugdelivery device is ready to use, but also results in a waste ofmedicament. The present disclosure describes priming procedures coveringboth possibilities.

These and other aspects of, and advantages with, the present disclosureswill become apparent from the following detailed description of thepresent disclosure and from the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will be explained in more detail withreference to the drawings.

FIG. 1 is a perspective illustration of one possible complete medicamentdelivery device containing the structural components of the presentdisclosure;

FIG. 2 shows a perspective illustration of the device of FIG. 1 wherethe cap is removed allowing attachment of a pen needle to the cartridgeholder;

FIG. 3 is an exploded view of the device of FIG. 1 .

FIG. 4 shows perspective views of the snap element with and without thefloating spline rotatably connected thereto;

FIG. 5 shows perspective views of the floating spline in both anassembled state and in a pre-assembled state;

FIG. 6 shows perspective views of the dose selector from both the distalend and the proximal end;

FIG. 7 is a perspective view of the piston guide;

FIG. 8 is a perspective view of the piston rod;

FIG. 9 is a perspective view of the of the driver;

FIG. 10 is a perspective exploded view of the nut and the clutch;

FIG. 11 is a perspective view of the housing of the dose settingmechanism;

FIG. 12 is a perspective view of the dose knob;

FIG. 13 illustrates a possible forced priming feature of the dosesetting mechanism;

FIGS. 14A-14E illustrate various positions of the snap element relativeto the dose selector;

FIG. 15 shows perspective views of an alternative snap element with andwithout an alternative floating spline rotatably connected thereto

FIG. 16 shows a perspective view of the alternative floating spline;

FIG. 17 shows perspective views of a first alternative dose selectorfrom both the distal end and the proximal end:

FIG. 18 shows perspective views of a second alternative dose selectorfrom both the distal end and the proximal end;

FIG. 19 shows a cross-sectional view of the second alternative doseselector from the proximal end and FIG. 19A shows an enlarged section ofthe cross-sectional view of FIG. 19 ; and

FIG. 20 shows a section of the alternative snap element having a snaparm with a lead-in chamfer.

DETAILED DESCRIPTION

In the present application, the term “distal part/end” refers to thepart/end of the device, or the parts/ends of the components or membersthereof, which in accordance with the use of the device, is located thefurthest away from a delivery/injection site of a patient.Correspondingly, the term “proximal part/end” refers to the part/end ofthe device, or the parts/ends of the members thereof, which inaccordance with the use of the device is located closest to thedelivery/injection site of the patient.

The dose setting mechanism 30 (see FIG. 3 ) of the present disclosurecan be used in a number of variously designed complete injectiondevices. One such embodiment of a complete injection device 10 isillustrated in in FIG. 1 , which is shown in the zero dose state asindicated by indicia 40 showing a zero through the window 3 a of housing3. FIG. 2 shows the device of FIG. 1 with cap 1 removed to expose thecartridge holder 2 and the proximal needle connector 7. Pen needle 4 isattached to the needle connector 7 through a snap fit, thread, Luer-Lok,or other secure attachment with hub 5 such that a double ended needlecannula 6 can achieve a fluid communication with medicament contained incartridge 8. The cartridge 8 is sealed at the proximal end by septum 8 aand with a sliding piston 9 at the opposite distal end.

As explained above, the dose setting mechanism 30 of the presentdisclosure is unique compared to other known pen-type injection devicesin that only a single component of the dose setting mechanism, namelydose selector 35, is primarily responsible for determining a finite setof predetermined fixed doses within a maximum allowable dose range.Moreover, this finite set of predetermined fixed doses can containfractional doses, meaning that each fixed dose does not have to be anequal multiple of the other fixed doses. For example, one fixed dosesetting can equal an equal multiple of a lower fixed dose plus afractional amount of that equal multiple.

The dose selector 35 is shown in FIG. 6 from both a proximal end viewand a distal end view. The outer surface of the dose selector has anumber of longitudinal grooves 35 a that are always engaged withlongitudinal splines 3 b located on the inner surface 3 d of housing 3(see FIG. 11 ). This engagement prevents relative rotation between thedose selector and the housing, but allows the dose selector to moveaxially relative to the housing. The outer surface of the dose selectoralso has connecting cut-outs 59 that permanently engage and lock withsnap fits 31 c on the dose knob 31 (see FIG. 12 ) such that the doseknob is axially fixed to the dose selector 35. These permanent snap fits31 e allow the dose knob to rotate relative to the dose selector duringboth dose setting and dose cancellation. At the distal end of the innersurface 35 b of dose selector 35 there is a set of fixed splines 54. Thenumber and relative spacing between of splines 54 is equal to the numberand relative spacing between of fixed splines 31 a located on the insideproximal end surface of dose knob 31. The reason for this equivalency,as explained more fully below, is to ensure the smooth transitionbetween the dose setting procedure and the initiation of the dosedelivery procedure when the dose knob disengages one set of splines andengages another set of splines. The space between each of the dose stopsis a multiple of the space between each of the radially projectinglongitudinal splines 52 on floating spline 34.

In one embodiment of the dose setting mechanism of the presentdisclosure the number of equally spaced splines 52 is chosen to allowfor eighty radial positions between knob and snap element. However, forergonomic and other reasons, the zero dose hard stop 55 d and the chosenmaximum dose hard stop 55 c limit the usable relative rotation of thedose setting knob to 270°. As such, this limited rotation means thatthere are effectively only 60 (sixty) usable radial positions (80splines×270°/360°). In one example, a customer may only want aninjection device having a maximum dose of 0.60 ml. This would then meanthat the sixty radial positions would lead to a raster (or increment) of0.01 ml. The user could select a fixed dose of 0.20 ml or 0.21 ml forexample, but not a dose of 0.205 ml. In most applications, a raster of0.01 ml is sufficient for any practical use.

In another possible embodiment, if the maximum dose was chosen to be0.30 ml using the 80 equally spaced splines 52, then this would be araster of 0.005 ml. This raster is typically finer than needed and analternative approach for this chosen maximum dose would be to have 40equally spaced splines instead of 80. The finer the raster the higher isthe likelihood that a binding/blocking problem will occur when thesplines on the dose knob engage with those on floating spline and thefixed splines 44 of snap element 33. A preferred acceptable radialmismatch should be below 4.5° when 80 splines are used.

As illustrated in FIG. 6 , there is a non-contiguous radially projectingcircumferential rib 56 also located on the inner surface of doseselector 35 that is selectively interrupted by a number of cut-outs 56 aat circumferential locations corresponding to dose stops 55 and topriming stop 55 a. The function of this rib 56 and the cut-outs 56 awill be explained in more detail below. The dose stops 55 corresponddirectly to the finite number of predetermined fixed doses that the dosesetting mechanism is capable of setting, including in some cases apredetermined fixed priming dose. One or more dose stops can be includedon the inner surface of dose selector 35. Preferably, the dose stops 55are formed as an integral part with the inner surface 35 b of doseselector 35 that can be manufactured as a single molded component. Asingle molded dose selector facilitates an important attribute of thedose setting mechanism of the present disclosure, which is the abilityto change a single component of the injection device to obtain adifferent set of finite predetermined doses. This is achieved bychanging the number and/or relative circumferential spacing of the dosestops on the inside of the dose selector.

The inner surface 35 b also has a zero dose hard stop 55 d. Thecircumferential spacing between each dose stop 55 and the zero dose hardstop 55 d is directly proportional to one of the finite set ofpredetermined fixed doses. As mentioned, in some cases, it is desirableto include a priming stop 55 a corresponding to a fixed priming dosethat allows a user to initially position the foot 42 a of piston rod 42in abutment with the distal end surface of piston 9 before a firstinjection is attempted. This priming step insures that the firstinjection accurately dispenses a dose of medicament that corresponds toone of the predetermined fixed dose settings. The dose stops 55 and thepriming stop 55 a are configured with a shape that facilitates dosesetting and dose cancelation, as will be explained in more detail below.FIG. 6 shows the dose stops having inclined surfaces 55 e and 55 f. Thisis in contrast to the zero dose hard stop 55 d that is configured as ahard stop.

Also shown in FIG. 6 on the inside surface of the dose selector is anoptional end of injection bump 55 b. During the dose delivery procedure,as the protrusion 45 rotates with the snap element relative to the doseselector the protrusion will eventually arrive at the end of injectionbump 55 b when the snap element returns to the zero dose setting. Theprotrusion will ride up and over the bump 55 b generating a notificationsignal to the user that the injection device 10 has returned to theinitial zero dose starting condition. This notification does notnecessarily indicate that that the expulsion of the set dose medicamentis reached, but it does signal to the user to begin the recommended 10second hold time of needle insertion to ensure complete delivery of thedose.

The setting of one or more of the predetermined fixed doses is achievedthrough the interaction of snap element 33 with dose selector 35. FIG. 4shows snap element 33 with and without the floating spline 34 rotatablyconnected to the outer surface 33 a of snap element 33. The snap elementcan be rotationally and axially connected to dose sleeve 38 throughsplines 48 and snap element 48 a. Protrusion 45 is arranged on aflexible arm 45 a and only engages the dose stops 55 and priming stop 55a during dose setting and dose cancellation. In other words, for reasonsexplained below, protrusion 45 does not engage the dose stops duringdose delivery as the snap element rotates in a counter-rotationdirection relative to the dose selector during dose delivery. A secondor blocking protrusion 46 is located on the outer surface 33 d at theproximal end of snap element 33. The location of this blockingprotrusion is selected so that it can abut the distal facing surface ofthe radially projecting rib 56 in the event dose delivery isinterrupted. As explained below, this abutment will prevent the doseknob from moving axially in the distal direction if during dose deliverythe user stops exerting a proximally directed axial force on the doseknob when the dose setting mechanism is in between two predeterminedfixed dose settings.

FIGS. 14A-14E illustrate the relative positions of the blockingprotrusion 46, the protrusion 45, the projecting rib 56 and the zerodose hard stop 55 d and the maximum dose hard stop 55 c. FIG. 14A showsthe dose setting mechanism in an initial zero set dose position wherethere is no axial force applied to the dose knob. i.e., a so-calledreleased state. Here blocking protrusion is abutting zero dose hard stop55 d preventing dialing a dose less than zero, i.e., turning the snapelement 33 in a clockwise direction. The protrusion 45 is on the backside of priming stop 55 a.

FIG. 14B shows the dose setting mechanism set with one of the finitepredetermined set doses (0.1 ml) set before the dose knob is pressed toinitiate the dose delivery procedure. Protrusion 45 is positioned on thefront side of dose stop 55 and blocking protrusion 46 is positioned onthe proximal side of projecting rib 56, but is in axial alignment withcut-out 56 a.

FIG. 14C shows the initiation of the dose delivery of the set 0.10 mldose of FIG. 14B prior to the beginning of the rotation of the snapelement 33. Here the dose selector 35 has now moved proximally relativeto the snap element 33 causing the blocking protrusion 46 to bepositioned on the distal side of projecting rib 56. This relativeposition change is only possible because to the cut-out 56 a beingaligned with the blocking protrusion 46. Dose stops 55 have now come outof radial alignment with protrusion 45, thus allowing snap element 33counter-rotate counter clock-wise relative to the dose selector as thedose delivery procedure continues.

FIG. 14D shows the relative position of the blocking protrusion 46 andthe projecting rib 56 in a condition where the user releases (removes)the proximally directed axial force on the dose knob during the dosedelivery procedure. The projecting rib 56 comes into abutment with theblocking protrusion 46 thus preventing distal axial movement of the doseselector. This also prevents the splines on the dose knob fromreengaging with fixed splines on the snap element. FIG. 14E illustratesthe interaction of the maximum dose hard stop 55 c with the blockingprotrusion 46 in cases where the user dials past the maximumpredetermined fixed dose setting. As illustrated the protrusion 45 hasmoved up and over the maximum predetermined fixed dose stop 55 and theblocking protrusion is in abutment with the maximum dose hard stop 55 cpreventing any further rotation of the snap element 33.

Snap element 33 also has a set of fixed splines 44, preferably that areformed integral to the snap element during the manufacture of the snapelement, for example during a molding process. These fixed splines 44 donot rotate or move axially relative to the snap element. The number andspacing of these splines 44 are equal to that of splines 54 on the innersurface of the dose selector and the splines 31 a on the inside of thedose knob. The function of splines 44 will be explained below. Snapelement 33 also can have a clicker 47, shown in FIG. 4 as a flexible armwith a radially directed nib. The clicker is configured to engage thesplines 31 a on the dose knob only during dose delivery such thatrotation of the snap element produces an audible and/or tactile feedbackas the clicker nib travels over the splines 31 a of dose knob 31. Duringdose setting the engagement of protrusion 45 with dose stops 55 andpriming stop 55 a also produce tactile and/or audible notification, butonly as each predetermined dose setting is reached. The number ofnotifications during dose setting is less than the number ofnotifications generated by the clicker 47 during dose delivery. This isbecause the clicker engages each of the equally spaced splines on theinside surface of the dose knob.

The snap element 33 also has an outer surface 33 a that accepts andaxially contains floating spline 34. The floating spline is axiallycontained to limit the axial movement of the floating spline relative tothe snap element. As indicated in FIG. 4 , the axial containment of thefloating spline to prevent movement distally and proximally is achievedby radial ribs 33 b, 33 c that define outer surface 33 a. Floatingspline 34 is shown in FIG. 5 where a preferred configuration is twohalves 34 a, 34 b that can be connected to each other after assemblyonto surface 33 a. The connection of the two halves can be through asnap fit shown as the combination of arms 49, 51 engaging detents 50 a,50 b, respectively. Regardless of the connection type, it is importantthat the engagement with the snap element 33 is such that the floatingspline and snap element can rotate relative to each other. The numberand spacing of the splines 52 on the floating spline 34 are equal tothat of splines 44, equal to splines 54 on the inner surface of the doseselector, and the splines 31 a on the inner surface of the dose knob.This is necessary because the floating spline 34 function as aconnector, as explained in more detail below, during dose delivery wherethe dose knob is prevented from rotating relative to the dose selector35. When the dose setting mechanism is assembled, the splines 54 on theinner surface of dose selector 35 are fully engaged or meshed withsplines 52. This meshing of splines 52 and 54 rotationally fixes thefloating spline 34 to the dose selector 35. Since the dose selector 35is splined to the housing 3 to prevent rotation, this results in thefloating spline 34 also being rotationally fixed to housing 3.

As shown in FIG. 5 , the terminal proximal end 52 a and terminal distalend 52 b of each spline 52 is chamfered to assist in the smooth meshingwith splines 31 a on dose knob 3 during the initiation of dose delivery.When the dose setting mechanism is assembled, the dose knob 31 issplined to the snap element 33 through meshing of only splines 44 andsplines 31 a on the dose knob. Because splines 44 are fixed rotationallyto snap element 33, rotation of dose knob 31 necessarily causes rotationof snap element 33 such that surface 33 a rotates relative to therotationally fixed inner surface 53 of floating spline 34. This rotationof the dose knob and snap element occurs during dose setting and isrelative to housing 3. During the initiation of the dose deliveryprocedure the dose knob is pressed in the proximal direction causing itto move axially relative to the snap element. This initial movementdisengages splines 31 a from splines 44 and causes splines 31 _(a) tothen engage floating spline 34. This new engagement of splines 31 _(a)and 52 then prevents the doe knob from rotating relative to the housing3 during dose delivery.

Details of dose knob 31 are illustrated in FIG. 12 . During assembly ofdose setting mechanism the dose knob is axially fixed and attached todose selector 35 through snap elements 31 c that are engaged withcorresponding cut-outs 59. This connection allows the dose knob torotate relative to the dose selector. The dose knob also has grippingsurfaces 31 d on the outer surface and includes a radially projectingrib 31 b that functions as an anti-roll feature, as well as, a leveragefeature to assist the user in setting or cancelling a dose.

FIG. 10 illustrates the nut 36 and the clutch 32 which are permanentlysplined to each other during assembly of the dose setting mechanismthrough a splined connection. The splined connection is established byconnection elements 37 of nut 36 and connection elements 71 of clutch32. This splined connection ensures that clutch 32 and nut 36 are alwaysrotationally fixed to each other during both dose setting and dosedelivery. This splined connection also allows the clutch and the nut tomove axially relative to each other. The sliding connection is necessaryin order to compensate for pitch differences between the threads 60 onthe piston rod 42 (see FIG. 8 ), the outer thread 39 on the dose sleeve38 (see FIG. 3 ) and the thread 67 on the driver 41 (see FIG. 9 ). Thesliding connection is necessary to compensate for the difference in thepitch of the thread between nut and the outer surface of the piston rodand the pitch of the thread between dose sleeve and body. The threadbetween driver and piston guide has basically the same pitch as thethread between piston rod and nut.

The proximal end of nut 36 has internal threads 70 that match threads 60of piston rod 42. The distal end of clutch 32 is configured as a dosebutton 72 and is permanently attached to distal end of the dose knob 31through engagement of connectors 73, which may also include snap locks,an adhesive and/or a sonic weld. This connection ensures that the clutchis both rotationally and axially fixed to the dose knob during both dosesetting and dose delivery.

As shown in FIG. 8 , in addition to threads 60 on the outer surface ofthe piston rod 42, there is also included two longitudinal flats 61 thatgive piston rod 42 a non-circular cross section. At the terminalproximal end is connector 62, shown as a snap fit, that connects with adisc or foot 42 a (see FIG. 3 ). At the distal end of piston rod 42 is alast dose feature of the dose setting mechanism, illustrated as anenlarged section 63. This enlarge section 63 is designed to stop therotation of nut 36 about threads 60 when the amount of medicamentremaining in the cartridge 8 is less than the next highest predetermineddose setting. In other words, if the user tries to set one of thepredetermined fixed dose settings that exceeds the amount of medicamentremaining in the cartridge, then the enlarged section 63 will act as ahard stop preventing the nut from further rotation along threads 60 asthe user attempts to reach the desired predetermined fixed dose setting.

The piston rod 42 is held in a non-rotational state relative to housing3 during both dose setting and dose delivery because it is arrangedwithin the non-circular pass through hole 64 in the center of piston rodguide 43 (see FIG. 7 ). The piston rod guide is both rotationally andaxially fixed to housing 3. This fixation can be achieved when thepiston rod guide is a separate component from the housing 3 asillustrated in the figures or the piston rod guide could be madeintegral with the housing. Piston rod guide 43 also has a connector 65configured to engage the proximal end of a rotational biasing member,shown in FIG. 3 as torsion spring 90, the function of which will beexplained below. This connection of the rotational biasing member to thepiston rod guide anchors one end in a rotational fixed position relativeto the housing.

The distal end of the rotational biasing member, for example torsionspring 90, is connected to connector 66 on the driver 41 (see FIG. 9 ).Driver 41 is connected and rotationally fixed with the inner surface ofdose sleeve 38 through splines 69 on the distal outer surface of thedriver. On the proximal end of driver 41 on the outer surface is threads67 that are engaged with matching threads on the inner distal surface ofthe piston rod guide 43. The thread between driver and piston guide hasa significantly different pitch than the thread between dose sleeve andhousing. The nut and the driver rotate together both during dose settingand dose cancellation and, as such, they perform essentially the sameaxial movement. However, this movement is independent from each other,i.e., the nut is turned by the clutch and performs an axial movement dueto the thread to the piston rod, while the driver is rotated by the dosesleeve and performs an axial movement due to the thread to the pistonguide. The driver is rotating during injection also, and so it activelymoves in the proximal direction during injection. But, the nut does notrotate during injection and as such does not perform an active axialmovement. The nut is only moving in proximal direction during injectionbecause it is being pushed axially by the driver. The rotating driverpushing the non-rotating nut causes the injection because the piston rodis pushed forward due to the threaded engagement with the nut.

If, for example, the thread of the nut had a higher pitch than thethread of the driver, the nut could not freely move in the distaldirection during dose setting because it would be hindered by the slowermoving driver. As such, this would cause drug to be expelled during dosesetting. Alternatively, if the thread of the nut had a significantlylower pitch than the thread of the driver, the driver would move awayfrom the nut during dose setting and the driver would not push the nutat the beginning of the injection already, but would do so only afterthe gap is closed. Accordingly, it is preferred that the pitch of thethread on the driver is equal or a slightly higher than the pitch of thethread on the nut. And, the thread between the dose sleeve and thehousing has a higher pitch than that of the nut and piston rod. This isdesirable because it yields a mechanical advantage that makes the dosedelivery process easier for the user. For example, when pushing the knoba distance of 15 mm, the piston rod only moves by 4.1 mm. This resultsin a gearing ratio of about 3.6:1. A lower gearing ratio would resultincrease the force the user needs to complete the injection.

As will be explained in more detail below, because the torsion spring isattached to the driver 41 and the driver is rotationally fixed to thedose sleeve 38, then rotation of the dose sleeve in a first directionduring dose setting will wind the torsion spring such that it exerts acounter rotational force on the dose sleeve in an opposite seconddirection. This counter rotational force biases the dose sleeve torotate in a dose canceling direction and provides the necessary forcefor the first fail-safe feature mentioned earlier.

The function of the complete injection device 10 and the dose settingmechanism 30 according to this disclosure will now be described.Injection device 10 is provided to a user with or without the cartridge8 of medicament positioned within the cartridge holder 2. If theinjection device 10 is configured as a reusable device, then cartridgeholder 2 is connected to housing 3 of the dose setting mechanism 30 in areleasable and reusable manner. This allows the user to replace thecartridge with a new full cartridge when all the medicament is expelledor injected from the cartridge. If the device is configured as adisposable injection device, then the cartridge of medicament is notreplaceable because the connection between the cartridge holder 2 andthe housing 3 is permanent. Only through breaking or deformation of thisconnection can the cartridge be removed from the injection device. Sucha disposable device is designed to be thrown out once the medicament hasbeen expelled from the cartridge.

The user first removes the cap 1 from the device and installs anappropriate pen needle 4 to the cartridge holder 2 using connector 7. Ifthe device is not pre-primed during the device assembly, or does nothave an automatic or forced priming feature as discussed above, then theuser will need to manually prime the device as follows. The dose knob 31is rotated such that the protrusion 45 engages a first dose stop, suchas the priming stop 55 a, which corresponds to a predetermined smallfixed dose of medicament. Rotation of the dose knob rotates protrusion45 on snap element 33 relative to dose selector 35 because the fixedsplines 44 are meshed with splines 31 a on the dose knob. During dosesetting an axial biasing member, shown in FIG. 3 as a compression spring91, which is located between the snap element and dose knob, exerts anaxial force on the dose knob in the distal direction to ensure thatsplines 44 and 31 a are and remain engaged during dose setting.

The injection device 10 of this disclosure can also have a so-calledforced or automatic priming feature, one embodiment of which isillustrated in FIG. 13 , where the clutch 32 is initially not rotatablyfixed to the dose knob 31. A sliding lock 80 is located between thedistal end of the clutch and the inside surface of the dose knob. Priorto using the dose setting mechanism, i.e., before a user could dial oneof the predetermined fixed dose setting, the sliding lock 80 wouldnecessarily need to pushed in the proximal direction such that is movesdistally relative to the dose knob. This axial movement causes the snapfingers 81 to engage the proximally facing surface 32 d of the clutchforming an irreversible locking relationship between the dose knob andthe distal end of the clutch. This locking relationship also causesteeth 32 c of clutch 32 and the corresponding teeth 82 of sliding lock80 to mesh and interlock such that the dose knob and clutch arerotationally fixed to each other. Before the sliding lock 80 is engagedwith the clutch, the clutch can be rotated, which also causes rotationof the nut, to cause the piston rod 42 to move axially relative to thehousing. The clutch is rotated until a visual observation and/or tactilenotification indicates that the foot 42 a located on the piston rod 42is in firm abutment with distal facing surface of the sliding piston 9.This abutment between the foot and the sliding piston will ensure thatan accurate dialed dose will be delivered out of the needle cannula.This rotation of the clutch is preferably performed during the assemblyof the injection device and likewise after ensuring abutment of the footwith the sliding piston 9, the manufacturing process would cause thesliding lock 80 to be pushed to the final, locked position. One possiblemeans to achieve rotation of the clutch would be to use a gripper with avacuum cup to turn the clutch. Alternatively, a slot or other connectorcould be designed into the distal surface of the clutch that cooperateswith a matching tool in order to engage and rotate the clutch. Thisoptional connector is shown as a slit 32 f in FIG. 13 .

The rotation of protrusion 45 and subsequent contact with one side ofthe priming stop 55 a, or for that matter any of the predetermined dosestops on the dose selector, will cause the flexible arm 45 a to flexradially inward allowing the protrusion 45 to ride up, over and down thereverse side of the dose stops 55 a, 55. This movement and contact ofthe protrusion 45 generates the audible and/or tactile notification thata dose stop has been reached during the dose setting procedure. The typeor level of notification can be modified by changing the design ofprotrusion 45, flexible arm 45 a, and/or configuration of the dose stops55 or priming stop 55 a. In some cases, it may be desirable to havedifferent notifications for each of the predetermined dose settings.Likewise, it may also be desirable to have the notifications during dosesetting be different than the notifications generated by clicker 47during dose delivery.

Returning to the priming procedure, once the priming stop 55 a isreached, the user may need to cancel the priming procedure and can do soby using the dose canceling procedure. This cancellation procedure alsoapplies to any of the predetermined dose settings. Dose cancellation isaccomplished by turning the dose knob in the opposite direction so thatthe protrusion 45 is caused to counter rotate in the opposite directionrelative to the dose stop 55 or priming stop 55 a. This will againgenerate a notification that can be the same or different as the dosesetting notification and/or dose delivery notification. Because the snapelement 33 is rotationally fixed to the dose sleeve 38, and the dosesleeve is threaded engaged to the inner surface of housing 3, rotationof the dose knob during dose setting and dose cancellation causesrelative rotation between the dose sleeve and the housing. The threadedconnection between the housing and the dose sleeve causes the dosesleeve, snap element, clutch, and dose knob to translate axially as thedose knob is rotated. During dose cancellation, these components rotateand translate axially in the opposite or proximal direction.

Rotation of the dose knob also causes rotation of nut 36 about threads60 on the outer surface of piston rod 42, which does not rotate andremains axially fixed relative to the housing 3 because of relativepitch differences in the threaded parts as explained above. The rotationof the nut relative to the stationary piston rod, which is supported byits contact with the sliding piston, causes the nut to translate orclimb up the piston rod in the distal direction. A reverse rotationduring dose cancellation causes the nut to translate in the reversedirection relative to piston rod. The distance traveled by the nut toachieve the desired dose setting is directly proportional to an amountof medicament that would be expelled if the dose delivery procedure wereinitiated and completed. Because the pitch of the threaded connectionbetween the dose sleeve and the housing is greater than pitch of thethreads on the nut, the dose sleeve, snap element, clutch and dose knobwill travel a greater axial distance than the nut as it climbs up ordown the piston rod. The difference in axial movement would normallybind the dose setting mechanism, but does not do so because thedifference in pitch is compensated for by the sliding splined connectionbetween the nut and the clutch, thus allowing the clutch to travelaxially a greater distance longitudinally than the nut. Duringinjection, the clutch pushes on the snap element and as such on the dosesleeve. This axial force causes the dose sleeve to turn due to thethread to the body. The dose sleeve will only start to turn when it ispushed, if the pitch of the thread is high enough. If the pitch is toolow the pushing will not cause rotation because the low pitch threadbecomes what is called a “self-locking thread.”

Rotation of the dose knob also causes rotation of the driver because ofthe splined rotationally fixed connection to the dose sleeve. Since thetorsion spring 90 is fixed at one end to the driver and at the other endto the piston rod guide, which in turn is fixed axially and rotationallyto the housing, the torsion spring is wound up increasing in tensionduring dose setting. As mentioned, the torque of the tension springexerts a counter rotational force on the dose sleeve. Preferably duringassembly of the dose setting mechanism, the torsion spring ispre-tensioned so that even at the zero dose condition the torsion springexerts a counter rotational force on the dose sleeve. The counterrotation force provides a first fail-safe feature of the dose settingmechanism. This first fail-safe mechanism prevents a user from setting adose that is not one of the finite set of predetermined dose settings.In other words, if a user is rotating the dose knob and the protrusion45 is between two dose stops, or between the zero dose hard stop and afirst dose stop 55 or a priming stop 55 a, and the user releases thedose knob, the counter rotational force of the torsion spring willreturn the protrusion to the last engaged dose stop or to the zero dosehard stop. Additionally, during a dose cancellation procedure thecounter rotational force will assist the user in rotating the dose knobback down to the next lower fixed dose setting or possibly all the wayback to the zero dose setting.

During dose setting, the dose knob translates out and away from thedistal end of housing 3. As the dose sleeve rotates and translates, theprogress of the dose setting (or dose cancellation) is observed inwindow 3 a of housing 3 as the printed indicia 40 on the dose sleevemoves past the open window. When a desired predetermined dose setting isreached the indicia for that dose will appear in the window. Because thedose stop 55 or the priming stop 55 a is engaged with the protrusion 45,the torsion spring will not have sufficient force to counter rotate theset dose to the next lower fixed dose setting. At this point theinjection device 10 is ready for a priming procedure or, if alreadyprimed, the delivery of the medicament to an injection site. In eitherthe case, the user will push on the dose knob in the proximal directionuntil the zero dose hard stop 55 d is reached and a zero dose indicia isobserved in the window. During a priming step the user will observewhether medicament is expelled out of the cannula 6 of pen needle 4. Ifno medicament is expelled this means the piston foot 42 a is not inabutment with the distal surface of sliding piston 9. The priming stepis then repeated until medicament is observed exiting the cannula.

The dose setting mechanism of the present disclosure can also have amaximum dose hard stop feature that prevents a user from setting a dosegreater than the highest predetermined dose setting. This is achievedthrough the use of a maximum dose hard stop 55 c that comes intoengagement with second protrusion 46 if a user dials, i.e. rotates thedose knob, past the dose stop corresponding to the highest predetermineddose setting. (see FIGS. 4 and 6 ). The engagement of the secondprotrusion with the maximum dose hard stop 55 c will prevent furtherrotation of the snap element. The maximum dose hard stop 55 c isconfigured with a shape such that the second protrusion 46 cannot berotated past the hard stop without deforming or breaking one or morecomponents of the dose setting mechanism. In the event a user dials pastthe last dose stop and engages the maximum dose hard stop 55 c with thesecond protrusion 46, a release of the dose knob will allow the torsionspring to counter rotate the dose sleeve, snap element and dose knobback to the last dose stop.

The dose setting mechanism also can have an anti-counterfeit oranti-disassembly feature that corresponds generally to the maximum dosehard stop. This anti-counterfeit feature is formed between a hard stopor hook 36 b located on the outside surface of nut 36 and a distalfacing end wall 32 b of a cut-out 32 a of clutch 32 (see FIG. 10 ). Asmentioned, the difference in pitch between threads 60 of the piston rod42 and the outer threads 39 of the dose sleeve 38 requires that theclutch translates further distally than the nut 36 as it climbs up thepiston rod 42 during dose setting. The cut-out 32 a and/or hard stop 36b can be positioned so that the axial translation of the clutch relativeto the piston rod is stopped at a predetermined position that generallycorresponds to the engagement of the second protrusion with maximum dosehard stop. The interaction of the hard stop 36 b with the distallyfacing wall 32 b will prevent further distal movement of the clutchrelative to the nut and thus can prevent disassembly of the dose settingmechanism. Typically, an attempt to disassemble the injection device isfor the purposes of replacing the expelled cartridge of medicament witha counterfeit cartridge to allow the injection device to be sold andreused as a faux new device. The anti-counterfeit feature inhibitsdisassembly if a person where to pull on the dose knob, which pulls onthe clutch, and which in turn pulls on the snap element 33 and dosesleeve 38. Although the threaded connection of the dose sleeve with theinside of the housing works as a primary disassembly feature, when thedevice is dialed to the maximum dose setting, this primary disassemblyfeature may not be sufficient to prevent disassembly. The secondarydisassembly feature where the hard stop 36 b engages facing wall 32 b asdescribed above can compensate for this insufficiency.

Once the dose setting mechanism is primed, the user then selects andsets a desired fixed dose by repeating the same steps used for primingexcept that the dose knob will be rotated past the priming stop 55 auntil the appropriate dose stop is engaged by the protrusion 45 and thedesired dose value appears in the window 3 a. In some cases, it ispreferred to have no indicia show in the window when dialing betweenpredetermined dose settings, while in other cases it is desirable toshow an indicia in the window that is indicative of a non-settable doseposition between the fixed dose settings.

Once one of the predetermined dose settings has been dialed on the dosesetting mechanism, the user can then exert an axial force in theproximal direction to initiate the dose delivery procedure. The axialforce exerted by the user overcomes the distally directed force exertedby the second biasing member 91 causing the dose knob 31, clutch 32 anddose selector 35 to move axially in the proximal direction relative tothe snap element 33 and housing 3. This initial movement disengages thesplines 31 a from splines 44 and causes engagement of splines 31 a withfloating spline 34, thus rotationally fixing the clutch and dose knob tothe housing through the splined connection between the floating spline34 and splines 54. Splines 54 and floating spline 34 remain engagedduring dose setting and during dose delivery even though the doseselector 35 moves axially with the dose knob 31 and relative to thefloating spline 34.

The initial axial movement of the dose selector relative to the snapelement causes the dose stops to come out of radial alignment withprotrusion 45 such that a rotation of the snap element relative to thedose selector would not allow the protrusion 45 to engage any of thedose stops, except of course the end of injection bump 55 b, whichprovides an audible and/or tactile notification, i.e., a so-called endof injection notification, to the user that the mechanical dose deliveryprocedure of the device is completed. As mentioned, this notificationalso informs the user to maintain the cannula in the injection site forthe recommend time, typically 10 seconds. Likewise, the initial axialmovement of the dose selector relative to the snap element also movesthe radially projecting rib 56 proximally relative to the secondprotrusion 46 such that the protrusion 46 faces the distal side of theprojecting rib 56 when rotation ofthe snap element relative to the doseselector occurs during the remaining dose delivery procedure. Theprojecting rib is able to move axially past second protrusion 46 becauseof the cut-outs 56 a that are in the projecting rib 56 in positionscoinciding with each dose stop 55 a, 55. At the end of injection,further rotation of snap element will cause the second protrusion toabut zero dose hard stop 55 d, which will prevent any further rotationof the snap element.

In addition to the end of injection feature described above, another endof injection notification feature can be incorporated as part of driver41. This alternative or additional end of injection feature alsoprovides tactile and/or audible notification to the user when themechanical dose delivery procedure is complete. One configuration ofthis end of injection feature is shown in FIG. 9 as the combination offlexible arms 68 a, 68 b. The flexible arm 68 b is loaded during dosesetting by a geometry of the inside of the dose sleeve 38. This holdsarm 68 b inside of the dose sleeve 38 because the flexible arm 68 b isbent to the right and inwards (see FIG. 9 ) and held in place by theflexible arm 68 a. When reaching zero after dose delivery, the flexiblearm 68 a is bent by a geometry of the dose sleeve to release flexiblearm 68 b. This is possible because the driver 41 is turned by the dosesleeve 38, so that both components have a purely linear movementrelative to each other due to the difference in the pitch of the tworespective threads 39 and 67.

As the user maintains the axial force on both the dose knob 31 and thedose button 72 during the continuation of the dose delivery procedure,the clutch 32 will abut the distal end of the snap element causing it tomove axially in the proximal direction. The clutch pushes on the snapelement. The snap element is fixed to the dose sleeve, so the clutchpushes on the dose sleeve. As the dose sleeve has a thread with asufficiently high pitch relative to the body, the axial force on thedose sleeve will cause the dose sleeve and as such the snap element toturn relative to the body, and by turning relative to the body it movesin the proximal direction. The dose selector slides into the housing,but does not rotate relative to the housing 3 due to the splinedengagement between spline 3 b and the groove 35 a. The rotation of thedose sleeve 38 also causes rotation of the driver 41 into the threadedconnection with piston rod guide 43, which drives the piston rodproximally and results in a concurrent de-tensioning of torsion spring90. The driver does not directly drive the piston rod. As the driverrotates, the driver moves in the proximal direction and pushes the nutforwards. As the nut doesn't turn, the driver pushes the nut and thepiston rod forward.

The nut 36 does not rotate during dose delivery because of therotationally fixed relationship with clutch 32 that is rotationallyfixed to the housing through rotationally fixed relationship of the doseknob, floating spline and the housing. The nut therefore can only moveaxially carrying the piston rod 42 with it because the piston rod isprevented form rotating by the non-circular opening 64 engaged with theflats 61 on the piston rod. The piston rod is moved axially the samedistance that the nut originally translated relative to the piston rodduring dose setting. This axial movement without rotation is caused bythe rotational and axial movement of the proximal end of the driver inabutment with flange 36 a of the nut. Axial movement of the piston rodcauses the sliding piston 9 to also move axially relative to the insidewalls of the stationary cartridge 8 forcing an amount of medicament outof the needle cannula 6 that is equivalent to the predetermined fixeddose that was set during the dose setting procedure.

If the user stops the dose delivery procedure by removing the axialforce on the dose knob the second fail-safe mechanism is activated.Removal of the axial force causes the compression spring 91 to bias thedose knob in the distal direction. If the user halts the dose deliverybetween two predetermined fixed dose settings, then the dose knob andthe axially fixed dose selector will both be prevented from movingproximally because the second protrusion 46 will come into abutment withthe distally facing side of projecting rib 56, which will stop theaxially movement of dose selector and dose knob. Without this abutmentof protrusion 46 with projecting rib 56, the dose selector would movedistally such that the splines 31 a would re-engage with splines 44 onthe snap element, thus placing the dose knob, clutch and nut back intorotational engagement with the snap element. The torque exerted on thesnap element through the driver would then counter rotate the nut, thusreducing the set dose by an unknown amount. This counter rotation wouldcontinue until the next lowest predetermined fixed dose setting isreached, where the corresponding dose stop would stop the counterrotation.

If on the other hand the dose delivery is halted at one of the lowerpredetermined fixed dose settings, the cut-out 56 a in the projectingrib 56 would allow dose selector to move distally such that the secondprotrusion 46 is positioned on the proximal side of rib 56. This wouldalso re-engage the splines 31 a of dose knob 31 with the fixed splines44 placing the dose knob, clutch and nut into rotational engagement withthe snap element as described above. However, because the cut-outs 56 aare only located at circumferential positions corresponding to the dosestops, there will be no counter-rotation of the snap element, and hencethe nut, because the dose stop and the first protrusion 45 are engaged.Because there is no counter rotation of the nut, there can be no unknownreduction in the set dose. Therefore, a resumption of the halted dosedelivery procedure will continue without any unknown decrease in the setdose, thus allowing the originally set predetermined dose to bedelivered.

Alternative designs of both the snap element and the floating spline areillustrated in FIGS. 15-16 , showing floating spline 134 as a singlecomponent piece, as opposed to the two-part clam shell designillustrated in FIG. 5 . To aid assembly of the floating spline 134 ontothe outer housing 133 a of snap element 133, a longitudinal slit 134 ais provided that allows the diameter of the floating spline to beenlarged and clipped onto the snap element between radial ribs 133 b,133 c, which define outer surface 133 a. In other words, the floatingspline is shaped like a split c-ring that can be expanded to open theslit such that it can be pressed or snapped over the outer surface ofthe snap element. This placement of the floating spline 134 preventsaxial movement distally and proximally relative to the snap element 133.To prevent rotational movement of the floating spline 134 relative tothe device housing, the proximal end has one or more radially outwardprojecting ribs 134 b that engage corresponding slots 135 d of doseselector 135. Dose selector 135 is rotationally fixed to the devicehousing through ribs 135 a. As with the design discussed above, snapelement 133 can rotate relative to the floating spline 134.

Snap element 133, again like the design described above, has a set offixed splines 144, preferably that are formed as an integral part orextension the snap element during the manufacture of the snap element.However, these fixed splines 144 are positioned in discrete sectionsaround the outside circumference of the distal end of snap element 133.This is in contrast to having the fixed set of splines be continuousaround the circumference of the snap element as illustrated in FIG. 4 .The fixed splines 144 do not rotate or move axially relative to the snapelement. The spacing of these splines 144 are equal to that of thesplines 31 a on the inside of the dose knob and function in anequivalent manner as splines 44 described below. Snap element 133incorporates a clicker 145 b extending proximally from radial protrusion145, as shown in FIG. 15 . The clicker 145 b is configured to engage agrooves or teeth 154 on the proximal surface of projecting rib 156 ofthe alternative dose selector 135 (see FIG. 17 ). In this alternativedesign of the snap element 133, splines 134 b remain engaged during dosesetting and during dose delivery even though the dose selector 135 movesaxially with the dose knob 31 and relative to the alternative designfloating spline 134.

The alternative dose selector 135 includes an alternatively designprotruding rib 156 that functions as an alternative second fail safefeature. In this alternative design, the rib 156 is no longerinterfering with the second protrusion 146, but with the protrusion 145,i.e. the protrusion on the flexible arm 145 a. In this alternativedesign, the axial position of this projecting rib 156 has changedrelative to rib 56 as shown in FIG. 6 . Once the user has started aninjection the dose selector is held at radial projecting rib 156 in amanner such that the knob 31 cannot jump out in the distal directionwhen a user removes axial force in the proximal direction.

The alternative projecting rib design 156 can be useful when torsionspring 90 is designed to be strong enough to maintain the injection evenwhen the user stops pressing on the knob, thus causing the snap elementto rotate relative to the knob. In the above described first design, thecompression spring 91 pushes the projecting rib 56 against theprotrusion 45, and the protrusion glides on the rib. But, when theprotrusion 45 reaches the cut-out 56 a in the projecting rib 56, thecompression spring 91 pushes the dose selector in the distal directionand the automatic injection stops. Even though the torsion spring isstrong enough to maintain the injection, if the user keeps the thumb onthe knob, applying a low force, the user could experience an uneveninjection force when the protrusion 45 reaches a cut-out 56 a, as thecompression spring could start to work. So, the first design of the failsafe mechanism can lead to unwanted effects when the torsion spring isstrong enough to maintain the injection. Additionally, the torsionspring could intentionally be just slightly too weak for an automaticinjection and this would require the user to keep pressing the knob tomaintain the injection. This would result in the user experiencing avery low dispense force because the spring assists in the injection.This could be called a “spring assisted injection”.

The advantage of a spring assisted injection over an automatic injectionis, that the user can influence the injection speed (as in a manualdevice). The advantage of a spring assisted injection over a purelymanual injection is, that the user does not need to apply a high forcefor the injection (as in an automatically injecting device). An intendedspring assisted injection may become an automatic injection (albeitpossibly very slow), when the force needed to expel the drug from thecartridge is lower than expected, or when the user presses slower thanexpected. As mentioned, the above described first design of the secondfail safe mechanism can lead to an uneven injection force when thedevice has a spring assisted injection.

The alternative second fail safe design to prevent the automaticinjection, illustrated in FIGS. 15 and 17 , includes sufficient frictionbetween the protrusion 145 and the projecting rib 156. When theinjection speed is dictated by the user (and not by the torsion spring),the protrusion 145 has a distance of about 0.5 mm to the radialprojecting rib 156. When the user releases the knob during injection,the compression spring 91 presses the rib 156 to the protrusion 145. Ifthe torsion spring is strong enough to maintain the injection, theprotrusion glides over the rib. In the alternative of the second failsafe design, the goal is to introduce sufficient friction between theprotrusion 145 and the rib 156. This could, for example, be caused byhaving grooves or teeth 154 located on the distal side of the rib 156,as shown in FIG. 17 , which could then interact with a proximallyprojecting tooth 145 b on the protrusion 145. The friction will stop therotation of the snap element 133 once the user releases the knob (orpushes the knob at a speed slower than the speed induced by the torsionspring). If the torsion spring is strong enough to maintain theinjection, the user can apply just the force to compress the compressionspring. In this case the protrusion has the above-mentioned distancefrom the rib and the injection speed is determined by the torsionspring.

The user can also apply a higher force to accelerate the injection. Inthis case, if the user releases the knob, the injection stops. When theuser releases the knob 31, the tooth 145 b on the still rotating snapelement 133 reaches the grooves or teeth 154 on the rib 156 before therotation is halted. There may be an unintended side effect if the userintends to keep the speed induced by the torsion spring by following theknob with the thumb, but presses with a force slightly lower than thatof the compression spring. In this case, the tooth may scrape over thetips. However, this unintended effect can be avoided by using anappropriate geometry leading to the friction between the protrusion andthe rib.

As mentioned, the knob jumps out when the knob is released at one of thepredetermined dose settings, where the rib has a cut-out. The likelihoodto release the knob at exactly one of those positions is low. However,if the user intends to press the knob only with the force necessary tocompress the compression spring, the knob could jump out at a cut out 56a.

Yet another alternative of the second fail safe design is possible andis illustrated in FIGS. 18-19 where a second alternative dose selector235 is shown that has no cut-outs in the protruding rib 256 at thepredetermined dose settings. FIG. 19A shows an enlarged section of thecross-sectional view of FIG. 19 . This is in contrast to the to theabove two designs previously described. Instead, the protruding rib 256has a reduced or indented rib section 256 a with a lead-in chamfer 256a. The protrusion 145 could also have a lead-in chamfer 145 c. When theknob 31 is pressed proximally to initiate an injection, the snap arm 145a and protrusion 145 on the snap element 133 has to flex to overcome thereduced rib 256 a. When this occurs, the user feels a tactical and/oraudible feedback in the form of a “click.” Once the protrusion haspassed the reduced rib 256 a, the compression spring 91 cannot press theknob 31 into the distal position any more, as the non-chamfered side 256d of the reduced rib 256 a is pressed against the non-chamfered side 145d of the protrusion 145 (see FIG. 20 ).

If the torsion spring 90 is strong enough, then the torsion spring canmaintain the injection, as the compression spring 91 cannot press theknob in the distal position at one of the lower predetermined fixed dosesettings. This second alternative design of the second fail safe featurewill also ensure that a spring assisted injection is smooth. As in theabove described design, the user can accelerate the injection using thisdesign, but the user cannot halt the injection. As illustrated in FIGS.18 and 19 , if the rib has a cut-out 256 b at the zero position, thecompression spring 91 will press the knob to the distal position at theend of the injection. However, if the rib does not have a cut-out at thezero position, the knob will stay in the proximal position relative tothe snap element. In this position the knob is linearly guided by thedose selector 235 through the floating spline 134 and cannot be turned.A rib without a cut out at the zero position thus provides a reuseprevention feature.

The reduction 256 a of the rib 256 at the predetermined fixed dosesettings and the chamfers 256 b can be chosen to adjust the strength ofthe tactical and/or audible click at the beginning of the injection. Fora device with a reuse prevention feature, as described above, theinitial click may be designed to be intentionally strong so as to avoidan unintended start of the injection (and as such an unwanted disablingof the device). In some circumstances it may be beneficial to combinethe above two alternative second fail safe designs into a single design.One possible way would be to use the first alternative described abovewhere the rib 256 would be manufactured without a cut out at the zeroposition to create a reuse prevention mechanism. Likewise, the secondalternative second fail safe design could include a friction surfacesimilar to surface 154 between the protrusion 145 and the rib 256. In apreferred design, the friction surface could have the function of anadjustable break, where if the user presses with a force lower than thatof the compression spring, the rib 256 is pressed against the protrusion145. The lower the force on the knob 31, the higher the force betweenthe rib 256 and the protrusion 145, and the higher the friction. Such anadjustable break could for example use rubber-like materials on thefriction surface, the protrusion or both. In this preferred embodimentthe user is able to both reduce the speed and accelerate the speed,which is given by the torsion spring. Of course, if the design of theprotruding rib included cut-outs, then this adjustable break featurewould not be applicable.

It is to be understood that the embodiments described above and shown inthe drawings are to be regarded only as non-limiting examples of thepossible designs of the safety assembly and such designs may be modifiedin many ways within the scope of the patent claims.

1. A dose setting mechanism comprising: a dose knob; a dose selector; aradial projecting rib positioned circumferentially on an inside surfaceof the dose selector; and a snap element comprising a protrusion,wherein the protruding rib has a reduced section that allows theprotruding rib to move axially relative to the protrusion to initiatedose delivery.
 2. The dose setting mechanism of claim 1, wherein thereduced section comprises a ramped surface that engages the protrusionto allow the reduced section to move axially relative to the protrusionto initiate dose delivery.
 3. The dose setting mechanism of claim 1,wherein: the knob moves proximally to initiate an injection, and theknob cannot move into a distal position while the protrusion is locatedat the reduced section once the protrusion has passed the reducedsection.
 4. The dose setting mechanism of claim 1, wherein anon-chamfered side of the reduced section engages with a side of theprotrusion once the protrusion has passed the reduced section to preventthe knob from moving in a distal direction.
 5. The dose settingmechanism of claim 1, wherein the protrusion on the snap element flexesto overcome the reduced section when the knob is pressed proximally toinitiate an injection.
 6. The dose setting mechanism of claim 1, whereinthe protruding rib has a cut-out at a zero position.
 7. The dose settingmechanism of claim 1, wherein the protrusion has a lead-in chamfer. 8.The dose setting mechanism of claim 1, wherein the reduced section isaligned with a dose stop provided on the dose selector.
 9. The dosesetting mechanism of claim 8, wherein the dose knob can only moveaxially relative to the snap element when the protrusion or a furtherprotrusion of the snap element is engaged with the dose stop of the doseselector.
 10. A dose setting mechanism comprising: a dose knob; a doseselector, a radial projecting rib positioned circumferentially on aninside surface of the dose selector; and a snap element having aprotrusion, wherein a release of the knob during an injection introducesfriction between the protrusion and the rib.
 11. The dose settingmechanism of claim 10, wherein the friction stops the injection.
 12. Thedose setting mechanism of claim 10, wherein the friction stops arotation of the snap element.
 13. The dose setting mechanism of claim10, wherein the protruding rib has a friction surface.
 14. The dosesetting mechanism of claim 13, wherein the friction surface comprises aplurality of grooves.
 15. The dose setting mechanism of claim 14,wherein the protrusion of the snap element comprises a clicker thatengages the plurality of grooves when the axial proximal force isreduced.
 16. The dose setting mechanism of claim 10, further comprisinga rubber-like material on at least one of a friction surface of theprotruding rib and the protrusion of the snap element.
 17. The dosesetting mechanism of claim 10, further comprising a torsion spring,wherein the torsion spring at least assists a user in providing adispense force for dispensing a medicament with the dose settingmechanism.
 18. The dose setting mechanism of claim 17, wherein thetorsion spring is strong enough to maintain an injection.
 19. The dosesetting mechanism of claim 10, wherein the dose selector is held at theradial projecting rib in a manner such that the knob cannot jump out ina distal direction when an axial force exerted on the dose knob isreduced once an injection has been started.
 20. The dose settingmechanism of claim 10, wherein the protrusion engages with the radialprojecting rib when an axial force exerted on the dose knob is reduced.